The objective of the present proposal is to use the 133Xe inhalation method of measuring regional cerebral blood flow (rCBF) to study brain behavior relations in normal aged individuals and in patients with Alzheimer's disease of senile onset, multi-infarct dementia and depression. During years 1 and 2 of the project, sensorimotor and cognitively mediated activation of hemispheric and regional cerebral blood flow, and the variables which affect the level and pattern of activation, in normal aged subjects will be investigated. During the third year of the project, the concomitant changes in cerebral blood flow and cognitive functions in patients with Alzheimer's disease of senile onset, multi-infarct dementia, depression, and in normal aged subjects will be investigated. Completion of the project will provide confirmation of the utility of the 133Xe inhalation method as a diagnostic tool in the study of the cortical dementias associated with the senium. It will provide otherwise unobtainable information about the effect of these processes on brain functioning in the geriatric population.